Miniature current overload fuse



April 1969 J. M. BORZONI 3,436,711

MINIATURE CURRENT OVERLOAD FUSE I Sh t I of 2 Filed Nov. 20. 3.967 e9 lz JnflBarmarzd I W WW a 6w JiaerzZ'F April 1969 J. M. BORZONI 3,436,711

MINIATURE CURRENT OVERLOAD FUSE Filed Nov. 26, 1967 Sheet 2 of 2 I J5 II 6% 9 J4 f/Oa 64L \w 'Qx xw i i9 c 1 Q United States Patent Ofiice US.Cl. 337-198 13 Claims ABSTRACT OF THE DISCLOSURE A minature currentoverload fuse is provided comprising an elongated body of insulatingmaterial and terminal pins extending transversely through the endportions of the insulating body, and projecting a relatively largedistance beyond the inner side thereof. The opposite or outer ends ofthe terminal pins preferably project a small distance beyond the outerside of the insulating body. At least the outer side of the intermediateportion of the insulating body has on the opposite longitudinal marginsthereof a pair of barrier-forming walls spaced apart a relatively smalldistance to prevent the entry therebetween of a human finger, or abarrier-forming wall or terminal pin of another similar fuse. A fuselink extends between the outer ends of the terminal pins which fuse linkis sized to be dropped into place between the barrier-forming walls andsoldered or welded to the terminal pins.

The present invention relates to a miniature current overload fusecapable of carrying substantial currents, such as currents as high asten or more amperes.

An overload fuse capable of carrying currents of the above magnitudecommonly comprises a sealed cylindr-ical glass envelope with cylindricalterminals projecting from the ends thereof and a fuse link extendingbetween the fuse terminals within the sealed cylindrical envelope.'Fuses of this type having current ratings of I-30 amperes commonly havelengths of the order of magnitude of over one inch and, together withthe mounting terminals with which they are associated, an overall widthof approximately one quarter inch and higher. Some of the disadvantagesof this type of fuse are the large space requirements for mounting thesame and difiiculty in easily determining a blown fuse by sight.

The present invention represents a marked improvement in overloadcurrent fuses of the ratings referred in that, among other reasons, afuse having a rating as high as 30 amperes can be made having a lengthwell under 4 inch, that is of the order of magnitude of the thickness ofan average human index finger, and a width of under 4 inch. Also, theterminals of the fuse can plug into socket openings transversely to thelength of the fuse body so the socket connector can be a much lessexpensive and less bulky support means than that needed for conventionalhigh current rated fuses. Moreover, the fuse of the invention isdesigned so that, despite the small size of the fuse, the fuse can beeasily and safely handled when installing or removing the same.

In accordance with the most preferred form of the invention, the fusehas an elongated body of insulating material, most advantageously athermosetting material such as melamine phenolic material, which is madewith a distinctive color indicating the rating of the fuse. A pair ofrelatively long and thick terminal pins extend transversely through theend portions of the elongated body and project a relatively largedistance beyond the inner side of the end portions of the insulatingbody so that they are readily receivable and supportable in the socketsof an electrical connector and so that there is an appreciable heatconducting area which can contact a Patented Apr. 1, 1969correspondingly large area of the metal sockets into which they extendwhich carry away the heat generated in the fuse by the large currentsinvolved. In the most preferred form of the invention, the length of theinsulating body is not greater and preferably less than the distance theterminal pins project beyond the inner side of the insulating body, sothat a maximum area of the terminal pins are exposed consistent with thestrength requirements of the fuse. The outer ends of the terminal pins,which are referred to as fuse connecting ends, project if at all only arelatively small distance beyond the outer side of the insulating body.A fuse link of substantially contrasting color to the insulating body isprovided which most preferably extends between bosses on the outer sideof the insulating body between the fuse connecting ends of the terminalpins. The fuse link will thus stand out sharply from the contrastingbackground supplied by the insulating body. The fuse link may be a thinstamping of fuse material with eyelets on the ends thereof adapted totit over the ends of the terminal pins where they are anchored theretopreferably by soldering the same thereto. The insulating body preferablyhas a depression in the center portion thereof so that the centerportion of the fuse link is substantially spaced from the insulatingbody.

Of great importance is the provision of a pair of spaced, confronting,outwardly extending, barrier-forming walls of insulating material on theopposite longitudinal margins of the outer side of at least theintermediate portion of the insulating body. The barrier-forming wallsproject outwardly beyond the insulating body a distance appreciablygreater than the fuse connecting ends of the terminal pins and the fuselink, so that the barrier-forming walls can be engaged by the fingers ofthe user on the laterally outwardly facing sides or the outer endsthereof without touching the conductive parts of the fuse on the outerside of the insulating body. The barrier-forming walls are mostadvantageously spaced apart a small distance so that a users finger, abarrier-forming wall or terminal pin of another identical fuse cannotfit or become wedged between the barrier-forming walls. The spacingbetween these walls is sufficient to allow the widest (i.e. highestcur-rent rated) fuse to be dropped between the barrierforming walls whenapplied over the fuse connecting ends of the terminal pins. Theinsulating body is most advantageously undercut to a substantial degreeso that there are shoulders provided for conveniently grasping the fuseto pull the same from an electrical connector.

Other advantages and features of the invention will become apparent uponmaking reference to the specification to follow, the claims and thedrawings wherein:

FIG. 1 is a perspective view of a miniature current overload fuseconstituting the most preferred form of the invention;

FIG. 2 is an exploded view showing the three basic components of thefuse of FIG. 1 before the final assembly thereof;

FIG. 3 is a longitudinal sectional view, somewhat enlarged, of thecomponent parts of the fuse shown in FIG. 2 just prior to a solderingoperation which secures the parts together;

FIG. 4 is a longitudinal sectional View corresponding to FIG. 3 of thecompleted fuse;

FIG. 5 is a vertical sectional view through the fuse of FIG. 4, takensubstantially along section line 5-5 thereof;

FIG. 6 is a horizontal sectional view through the fuse of FIG. 4, takensubstantially along the line 6-6 thereof;

FIG. 7 is a horizontal sectional view through the fuse of FIG. 4, takensubstantially along the line 7-7 there- FIG. 8 is a fragmentary planview of a fuse block having a number of fuses like that shown in FIGS. 1through 7 inserted therein; and

FIG. 9 is a fragmentary, partly broken away view of the portion of thefuse block shown in FIG. 9, showing the construction of the socketswhich receive one of the fuses thereof.

Referring now more particularly to FIGS. 1-7, a miniature currentoverload fuse 1 of the invention is there illustrated comprising ahorizontally elongated insulated body 2 having a relatively narrow upperflange-forming portion 2a and a reduced main body or skirt-formingportion 2b. In the most preferred form of the invention, both theflange-forming and main body-forming portions of the insulating bodyhave a length at least in the neighborhood of about twice the height andwidth of the main body portion 2b thereof. The end portions of theinsulating body 2 have vertically or transversely extending openings 4-4within which are anchored a pair of terminal pins 6-6. The terminal pins6-6 project a substantial distance downwardly from the bottom or innersurface 7 of the insulating body, most advantageously a distance of atleast equal to and preferably a substantially greater distance than theheight of the main body portion 2b of the insulating body. The upper orouter ends of the terminal pins 6 are fuse connecting ends of the pinswhich most advantageously extend through and project a short distancebeyond the flat to-p surfaces of a pair of bosses 8-8 projectingupwardly or outwardly from the outer fiat surface 9 of the insulatingbody.

Each of the terminal pins 6-6- preferably has a main cylindrical bodyportion, the upper section 6a thereof being located Within the openings4-4 and terminating in a downwardly flaring skirt 6b having an irregular(that is non-circular) cross section. The bottom section 6a of the maincylindrical body portion of the terminal pins have a thickness which ispreferably a substantial portion of the width of the main body portion2b of the insulating body, preferably at least in the neighborhood ofonehalf the width thereof. The main upper section 6a of the maincylindrical body portion of each terminal pin is most advantageouslyflush with upper surface of the associated insulating body boss 8 andterminates in a reduced end portion 6c which projects upwardly arelatively small distance beyond the top of the boss 8. The reduced endportion 60 of each terminal pin most advantageously terminates in anoutwardly tapering or chamfered .portion 6a. The bottom of each terminalpin 6 similarly terminates in a chamfered portion 62.

The insulating body 2 which is preferably made of a thermosettingsynthetic plastic 'mateiral most advantageously a melamine phenolicmaterial, which is transfer molded around the terminal pins. Themelamine phenolic material gives off an arc quenching vapor under heatedconditions prevailing in ,the fuse when the fuse blows. The terminalpins are preferably made of copper coated with a suitable coating ofmetal, such as a .00005 inch layer of Bright alloy plate, an alloy oftin, zinc and copper sold under the trademark Albaloy which protects thecopper pins during the molding operation and provides for long shelflife.

Extending between the reduced end portions 6C6C of the terminal pins 6-6is a fuse link 10 made of a material which melts when a prolongedcurrent greater than the fuse rating flows therein. The fuse link 10most advantageously is a fiat plate-like member having a very thinintermediate portion 10a with a width or thickness which varies with therating of the fuse involved, and thin end portions 10b-10b which formeyelets having openings 100-100 which fit around the reduced endportions 60-60 of the terminal pins 6-6. The flat faces of the fuse linkpreferably seat upon the flat upper surfaces of the bosses 8-8. Thereduced end portions 60-60 of the terminal pins preferably extend abovethe upper surface of the fuse link so that rings 11-11 of solder 4(FIGS. 2 and 3) can be positioned about the pins above the fuse link andmelted to form dome-shaped blobs 11'11' of solder (FIGS. 1 and 4)extending over the chamfered portions 6d-6d of the terminal pins, firmlyto secure the fuse link to the terminal pins.

The central portion of the fuse link 10 which is to melt is mostadvantageously spaced an appreciable distance from the insulating body 2by a recess 14 formed in the upper surface 9 of the insulating body.

In the most preferred form of the invention, the main body portion 212of the insulating body has rounded protuberant ends sections 16-16 whichgradually merge with a reduced central section 17. The reduced centralsection 17 forms a relatively wide undercut or shoulder-forming portions18-18 on the outwardly laterally facing sides of the insulating body atthe bottom of the flange forming portion 2a thereof, so that the fusemay be readily grasped to insert the same into or remove the same from afuse block 20 (FIGS. 8 and 9).

The upper or outer side of the intermediate portion of the insulatingbody 2 has on the opposite longitudinal marginal portions thereof a pairof confronting, transversely spaced, vertical barrier-forming walls15-15. The barrier-forming walls 15-15 most advantageously form anoutward extension of the flange-forming portion 2a of the insulatingbody 2. The barrier-forming walls preferably terminate short of the endportions of the fuse body, so that the upper ends of the terminal pins6-6 can be fully exposed to receive a soldering tool for soldering thefuse and the terminal pins tOgether. (The broadest aspect of theinvention envisions the barrier-forming walls extending completelyaround the margin of the fuse link where a solder or welding operationis carried out by induction heating techniques.) The barrier-formingwalls form a very important feature of the fuse body because they aredesignated to enable the fuse to be handled during insertion and removalof the fuse from the terminal block 20 without shock and burn hazards tothe person handling the fuse.

The barrier-forming walls most advantageously project substantiallyabove the uppermost or outermost portion of the adjacent conductiveparts of the fuse namely, the terminal pins 6-6, the fuse link 10 andthe solder 11'11'. Also, the barrier-forming walls are spaced apart adistance much less than the average thickness of a human index fingerand less than the thickness of the barrier-forming walls or the terminalpins, so that the barrier-forming walls minimize the possibility thatthe user can touch the current-carrying portions of the fuse by bringinghis finger down against the upper end of the fuse, and thebarrier-forming walls and terminal pins of other identical fuses cannotbecome wedged between the walls when identical fuses are stored in alarge mass. Of equal significance is the fact that the laterallyoutwardly facing surfaces 1515' (FIG. 5) of the barrier-forming wallsare in vertical planes which are spaced appreciably from the outermargins of the fuse link 10, the solder 11'11' and the upper ends of theterminal pins 6-6, so that a person grasping the fuse and inserting thesame into a fuse block will have his fingers spaced an appreciabledistance from the current carrying portions of the fuse. (It can beappreciated that if a fuse is inserted within a fuse block where thecircuit into which the fuse is being placed has a short circuit therein,substantial currents can flow momentarily which can generate appreciableamounts of heat which could burn a person inserting the fuse into thefuse block unless the current carrying portions of the fuse are spacedan appreciable distance from the portions of the fuse engaged by theusers fingers.)

The barrier-forming walls 15-15 are also preferably spaced apart adistance greater than the width of the widest fuse link to be used withthe fuse body so that the fuse link 10 is spaced from all portions ofthe insulating body to assure consistent fuse blowing characteristicsand so that the fuse link can be readily dropped ihto place between thebarrier-forming walls upon the terminal pins 6-6.

An especially important feature of the present invention made possibleby the design of the fuse parts and their relationship is the extremelysmall size of the fuse for the current rating thereof. For example, acommercial form of the fuse of the invention rates at 30 amperes has anoverall length of only about .625 inch, an overall width of about .225inch and an overall height (including the barrier-forming walls butexcluding the pin lengths) of about .312 inch. In application of thepresent invention, it is preferred to standardize all portions of thefuse except the fuse link 2 which will vary in width, thickness ormaterial, depending upon the fuse rating. It is of great importance toprovide relatively large heat conducting area for carrying heat awayfrom the fuse without making the fuse bulky, particularly in length andwidth. This is made possible by the use of relatively thick terminalpins which project an appreciable distance beyond the inner surface ofthe insulating body and the use of metal socket terminals which engagethe terminal pins over most of the projecting positions thereof. Forexample, in the commercial form of the invention, the projecting portionof the terminal pins have a diameter of the order of magnitude of about/8 inch and a projecting length of about /3 inch. To make the mosteificient use of the insulating material, the pins were embedded in theinsulating body for about inch of their length. The length andconfiguration of the insulating body tend to minimize fatigue failuredue to frequent cycling of the fuse between no-load and near rated load.

FIGS. 8 and 9 illustrate the terminal block 20 into which :a number offuses like that shown in FIGS. 1 through 7 can be supported inrelatively close relation. The fuse block 20 has a pair of metal sockets2222 (FIG. 9) into which the projecting ends of the terminal pins 6-6 ofa fuse 1 can be snugly inserted. The metal sockets 2222 make extensivephysical and electrical contact with the terminal pins 66 of theassociated fuse so they make a good low resistance high heat conductingcontact therewith. The sockets 22-22 are shown embedded within a body 23of insulating material forming the main body portion of the fuse block20.

It should be understood that numerous modifications may be made in themost preferred form of the invention described above without deviatingfrom the broader aspects thereof.

I claim:

1. A miniature current overload fuse comprising: an elongated body ofinsulating material of a length which is substantially less than inch soit is of a size not substantially greater than the thickness of anaverage human finger, the end portions of said insulating body having apair of transversely extending openings passing therethrough, terminalpins anchored in said openings and projecting beyond the inner side ofthe end portions of the insulating body a distance where they arereadily receivable and supportable in the metal sockets of an electricalconnector and present a heat radiating area capable of adequatelyconducting heat to said metal connector sockets for prolonged currentsof at least ten amperes, said pins having fuse connecting end portionspositioned adjacent the outer side of said insulating body, at least theouter side of the intermediate portion of said insulating body having onthe opposite longitudinal marginal portions thereof a pair of spacedconfronting barrierforming walls which project outwardly of saidinsulating body so the ends thereof are spaced from the fuse connectingends of said terminal pins, and a fuse link adapted to melt when a givenprolonged overload current flows therethrough and having end portionsrespectively connected to said fuse connecting ends of said terminalpins and a bridging intermediate portion passing between saidbarrier-forming walls well below the tops thereof, the

fuse link having a central portion which is first to melt which centerportion is spaced from said insulating body to be completely out ofcontact with the heat absorbing parts of the fuse.

2. The miniature fuse of claim 1 wherein said barrierforming walls arespaced apart a distance less than the thickness of either of saidbarrier-forming walls or terminal pins, so that a barrier-forming wallor terminal pin of a fuse similar to said miniature fuse cannot enterthe space between said barrier-forming walls.

3. The miniature fuse of claim 1 wherein the outer longitudinal marginsof said barrier-forming walls are in planes substantially spaced fromthe nearest margins of the fuse connecting ends of said terminal pinsand said fuse link, whereby said barrier-forming walls can be graspedwithout touching the conductive parts of the fuse.

4. The miniature fuse of claim 1 wherein said barrierforming wallsproject outwardly a substantial distance from said terminal pins andsaid fuse link, and said planes of the outer longitudinal margins ofsaid barrier-forming walls are substantially spaced from said terminalpins and fuse link, the barrier-forming walls spacing the fingers of aperson touching the outer ends thereof or grasping the barrier-formingwalls a substantial distance from the terminal pins and the fuse link toavoid burning the users fingers even under short circuit currentconditions.

5. The miniature fuse of claim 1 wherein both longitudinal outer sidesof said insulating body have substantially undercut portions formingshoulders enabling the fuse to be grasped and pulled from an electricalconnector.

6. The miniature fuse of claim 1 wherein said barrierforming wallsterminate short of the fuse connecting ends of said terminal pinswherein the pins are substantially fully exposed for readily attachingthe fuse link thereto.

7. A current overload fuse comprising a body of insulating materialhaving a horizontally elongated cross section, the end portions of saidinsulating body having a pair of vertically extending openings passingtherethrough, vertically extending terminal pins anchored in saidopenings which terminal pins project substantially vertically from thebottom of said insulating body so that they are readily receivable andsupportable in the sockets of an electrical connector, the upper ends ofsaid terminal pins projecting a relativelty small distance above theadjacent upper surface of said insualting body and forming fuseconnecting ends of the pins, at least the upper side of the intermediateportion of said insulating body having on the opposite longitudinalmarginal portions thereof a pair of transversely spaced confrontingvertical barrierforming walls which enable the user to grasp the fusewithout touching the conductive parts of the fuse, and a fuse linkextending adjacent the top of said insulating body between saidbarrier-forming walls and connected between the fuse connecting ends ofsaid terminal pins, the spacing between said barrier-forming walls beinggreater than the corresponding width of the intermediate portion of thefuse link so the link can be dropped between the barrier-forming wallsupon the fuse connecting ends of the terminal pins and beingsubstantially less than the thickness of a human finger, and the top andouter margins of said barrier-forming walls being positioned in planesspaced from the corresponding outer portions of the fuse connecting endsof said terminal pins and said fuse link, wherein the barrier-formingwalls keep the user from touching the conductive parts of the fuse whenit is grasped to insert the same or remove the same from an electricalconnector.

8. The fuse of claim 7 wherein said body of insulating material whenheated under heavy overload conditions gives off an arc quenching gas.

9. The fuse of claim 7 wherein the portion of said body of insulatingmaterial which said fuse link overlies is made of a color whichcontrasts sharply with the color of the fuse link.

10. The fuse of claim 7 wherein the fuse link has eyelets at the endsthereof which fit around the fuse connecting ends of said terminal pinsat a point below the uppermost parts of said terminal pins, and saidfuse link being physically and electrically connected to said terminalpins project downwardly beyond the bottom of portions of said fuse linkand melted intimately to bond the fuse link to the terminal pins.

11. The fuse of claim 7 wherein the length of said insulating body is atleast in the neighborhood of twice the height and width of theinsulating body, and said terminal pins project downwardly beyond thebottom of the insulating body a distance at least comparable to theheight of the insulating body.

12. In combination: a fuse support having at least two metal socketstherein; and a current overload fuse comprising a body of insulatingmaterial having a horizontally elongated cross section, terminal pinsanchored to and extending vertically through the end portions of saidinsulating body, the terminal pins having a width which is at least inthe neighborhood of one half the width of the main portion of theinsulating body, the terminal pins projecting downwardly from the bottomof said insulating body a distance at least comparable to the height ofthe insulating body, said terminal pins extending into said metalsockets where they are engaged thereby for substantially the full lengthof the downwardly projecting portions thereof, and a fuse link extendingbetween the upper ends of said terminal pins.

13. A current overload fuse comprising a body of insulating materialhaving a bottom portion of reduced cross section leaving downwardlyfacing shoulders on the opposite sides thereof which aid the user ingrasping the insulating body to insert the same into or remove the samefrom a fuse block, terminal pins anchored to and extending through theend portions of said insulating body and projecting a relatively largedistance from the inner side of said insulating body so they are readilyreceivable and supportable in sockets of an electrical c011- nector, apair of bosses projecting transversely from end portions of the outerside of the insulating body and through 'which bosses said terminal pinsproject outwardly a relatively short distance, a fuse link extendingbetween the outer faces of said bosses and having eyelets which fitaround the portions of said terminal pins projecting beyond said bosses,and bodies of solder extending between the outer surfaces of said eyeletportions of said [fuse link and the adjacent surfaces of said terminalpins.

References Cited UNITED STATES PATENTS 2,117,346 5/1938 Millis 3371942,316,163 4/1943 Hignutt 337198 2,830,156 4/1958 Burgess 3372223,027,438 3/1962 Reutter 337-l98 X 3,110,787 11/1963 Borzoni 337-260 XBERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

U.S. Cl. X.R. 337-255

